Packed beds are known in the art for their applications in gas-liquid separations such as air from water or absorption/desorption processes such as the absorption of a particular gas from an exhaust gas. The performance of packed beds, also referred to as packed columns, is primarily given by the porosity of the material used for the packing, its total surface area of the packed bed, as well as the total height of the column. Typically, a gas and a liquid are directed through stationary packed beds in counter-current flow direction to one another, because a higher separation efficiency can be achieved in a counter-current-flow process compared to co-current-flow process.
In stationary packed beds the liquid passing through the packing is only acted on by gravity, which results in the fact that the columns must be designed with a considerable height in order to achieve a desired degree of separation.
Rotating packed beds, as for example first presented by its initial inventor in U.S. Pat. No. 4,400,275 consists of a packing arranged on a shaft, through which gas and liquid are passed. The rotation of the packed bed on the shaft allows to increase the specific surface area per volume acting in the separation process such that the total volume of the packed bed for a given performance may be smaller compared to that of a stationary packed column. While the mass transfer coefficient for a rotating bed is beneficially increased, the pressure loss suffered across the bed however is increased.
In a stationary packed column, gravity acts on the liquid flow through the packing and buoyancy of the gas allows it to flow through the packing in upward direction. A rotating packed bed on the other hand requires additional energy for acceleration of the gas through the packed bed while overcoming the frictional forces as well as to operate the rotating system.
In D. P. Rao, A Bhowal, P. S. Goswami, “Process Intensification in Rotating Packed Beds: An Appraisal”, Ind. Eng. Chem. Res 2004, 43, 1150-1162, a rotating packed bed is presented, where gas introduced into the casing of the rotating bed enters at the peripheral tip of the rotating shaft and flows radially inward to the rotor's eye, where it leaves the apparatus through an outlet pipe. The liquid is fed in the form of a droplet spray or jet into the packed bed at the eye of the rotor, passes over the packing under the influence of the centrifugal force in a radially outward direction, and leaves the apparatus via an outlet pipe at the periphery of the rotating packed bed. Parameters, which determine the efficiency of a separation process due to the rotation, such as throughputs, gas flow, liquid flow, pressure drop, flooding, mass transfer coefficient on the gas- and liquid-side, and power requirements, are discussed.
U.S. Pat. No. 6,884,401 discloses a rotating packed bed with an inlet for a high viscosity liquid at a point near the axis of the rotating shaft and an outlet for the liquid at the periphery of the bed. An inlet is provided for a gas to pass radially inward through the rotating packing.
EP 2018900 discloses the use of a rotating bed for the degassing of a liquid, where a vacuum is applied to the interior region of the rotating packed bed via a gas outlet at the axis of the rotating bed's shaft. The degassed liquid is passed over the packing in a radially outward direction and can exit the device through an outlet near its periphery.